In the past, hydrocracking processes of heavy oil such as residual oil or vacuum gas oil (VGO) contributed to increased production of as well as to desulfurization of an intermediate fraction including kerosene and gas oil through reasonable cracking thereof by loading a part or all of reactors with hydrocracking catalysts containing a crystalline aluminosilicate (referred to hereinafter as zeolite).
It has been well known that a catalyst comprising an iron-containing zeolite obtained by treating zeolite with an iron salt was particularly excellent for a hydrocracking activity because deterioration control thereof caused by coke formation is capable through the increased hydrogen transfer capability (for examples, Patent literatures 1 and 2).
However, the hydrocracking catalyst comprising the iron-containing zeolite has had the difficulty of yielding high selectivity of an intermediate fraction in the range of high cracking activity thereof, and produced a plenty of a light fraction such as naphtha since the increased production of the intermediate fraction showed signs of leveling off as a result of an over cracking.
Further, it was also of problem that the cracking activity of a heavy fraction (343 deg C.+, a boiling point of the fraction is higher than 343 deg C.) was particularly low.
More further, in the case of not in harmony between a hydrocracking activity and a hydrodesulfurization activity, a sulfur content in the intermediate fraction comprising mainly kerosene and gas oil resulted in high and a second treatment of the intermediate was required additionally.
Therefore, so as to improve selectivity for an intermediate fraction catalysts have been modified by treating zeolites with excessive steam (a high temperature treatment under steam atmosphere) or with acid in a low pH area, therefore a part of the zeolite was destroyed and a certain volume of mesopores was formed so as to be space for cracking a heavy fraction.
However, the above modification methods resulted in destruction of the framework of the zeolite, accordingly the formation of enough numbers of mesopores resulted in deteriorating the crystallinity thereof.
Therefore, there was of problem that the hydrocracking activity was not demonstrated adequately because of decreasing of the surface area thereof due to the crystallinity deterioration of the zeolite.
Patent literature 1: Japanese Patent Publication No. Heisei 6 (994)-074135
Patent literature 2: Japanese Patent Laid-Open Application No. 2000-86233
Patent literature 3: Japanese Patent No. 1739396